According to the prior art, automatic transmissions, in particular for motor vehicles, comprise planetary gearsets which are shifted by means of frictional or shifting elements such as clutches and brakes and which are usually connected with a starting element that can operate with slip and is optionally provided with a bridging clutch, such as a hydrodynamic torque converter or a flow clutch.
Automatically shifted vehicle transmissions of planetary structure in general have been described many times in the prior art and are constantly undergoing further development and improvement. Such transmissions should have a sufficient number of forward gears and a reverse gear, and transmission ratios that are very well suited for motor vehicles and have a large overall spread and appropriate step intervals. Furthermore, they should enable a high starting transmission ratio in the forward direction and should possess a direct gear and be suitable for use both in passenger cars and in utility vehicles. In addition these transmissions should entail as little structural complexity and cost as possible, in particular requiring only a small number of shifting elements, and should avoid double shifts for sequential shifting operations so that for shifts in defined gear groups in each case only one shifting element is changed.
A multi-gear automatic transmission of this type is described, for example in WO 2006/074707 A1 by the present applicant. It comprises essentially a drive input shaft and a drive output shaft arranged coaxially with one another, a total of four single planetary gearsets and five frictional shifting elements. By selective engagement in each case of three of the five frictional shifting elements made as clutches and brakes a total of eight forward gears can be engaged without group shifts, i.e. they can be engaged or disengaged in such manner that on changing from one gear to the next-higher or next-lower gear, in each case only one of the previously engaged shifting elements is disengaged and one previously disengaged shifting element is engaged.